- 4566 -
BLACKHOLES - newest ones found? -
Using the Hubble Space Telescope, astronomers have discovered the
closest massive black hole to Earth ever seen, a cosmic titan "frozen in
time." This "intermediate-mass
black hole," could serve as a missing link in understanding the connection
between stellar mass and supermassive blackholes.
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- BLACKHOLES -
newest ones found?
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- The black hole appears to have a mass of
around 8,200 suns, which makes it considerably more massive than stellar-mass
black holes with masses between 5 and 100 times that of the sun, and much less
massive than aptly named supermassive black holes, which have mass millions to
billions that of the sun. The closest stellar-mass black hole scientists have
found is called “Gaia-BH1”, and it sits only 1,560 light-years away from us.
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- The newly found intermediate-mass black hole
dwells in a spectacular collection of about
ten million stars called Omega Centauri, which sits around 18,000
light-years from Earth. The fact that
the "frozen" black hole appears to have stunted its growth supports
the idea that Omega Centauri is the remains of an ancient galaxy cannibalized
by our own galaxy.
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- This would suggest Omega Centauri is
actually the core of a small, separate galaxy whose evolution was cut short
when the Milky Way swallowed it. If this event had never happened, this
intermediate black hole may have possibly grown to supermassive status like the
Milky Way's own supermassive black hole, Sagittarius A* (Sgr A*), which has a
mass 4.3 million times that of the sun and is located is 27,000 light-years
from Earth.
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- Scientists have known for some time that not
all black holes are created equally. While stellar-mass black holes are known
to form via the collapse of stars with at least eight times the mass of the
sun, supermassive black holes must have a different origin. That's because no
star is massive enough to collapse and leave a remnant millions of times as
massive as the sun.
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- Therefore, scientists propose that
supermassive black holes are born and grow due to merger chains of
progressively larger and larger black holes. This has been evidenced by the
detection of ripples in spacetime, called gravitational waves, emanating from
black hole mergers.
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- This process of black hole mergers and
growth, combined with the vast gap in mass between stellar-mass black holes and
supermassive black holes, means there should be a population of mid-size black
holes.
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- Yet, these intermediate-mass black holes
with masses between a few hundred and a few thousand times that of the sun
have, for the most part, seem to have avoided detection. That's because, like
all black holes, these mid-sized cosmic titans are marked by outer boundaries
called “event horizons”.
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- The “event horizon” is the point at which
the gravitational influence of a black hole becomes so immense that not even
light is fast enough to escape it. Thus, black holes are only visible in light
if they are either surrounded by matter to feed on, which glows while heating
up, or rip apart and feed on an unfortunate star in a so-called "Tidal
Disruption Event" (TDE).
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- Intermediate black holes, like the one in
Omega Centauri, aren't surrounded by a lot of matter and feeding. That means astronomers have to be a little
bit cunning when hunting for such black holes. They use the gravitational
effects these voids have on matter, like stars that orbit them or on light
passing through them.
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- The hunt for this intermediate black hole
began in 2019. The researchers wanted to
find rapidly moving stars in Omega Centauri that would prove the star cluster
has a massive, dense or compact "central engine" black hole. A
similar method was used to determine the mass and size of Sgr A* using a
fast-moving population of stars at the heart of the Milky Way.
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- Using over 500 Hubble images of this star
cluster built a vast database of the motions of stars in Omega Centauri,
measuring the speeds of about 1.4 million stars. This ever-repeating view of
Omega Centauri, which Hubble conducted not out of scientific interest but
rather to calibrate its instruments, was the ideal data set for the team's
mission.
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- Looking for high-speed stars and
documenting their motion was the proverbial search for a needle in a
haystack". The team ultimately
found not one but seven "needle-in-haystack stars," all moving at
rapid velocities in a small region at the heart of Omega Centauri.
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- The rapid speed of these stars is caused by
a concentrated mass nearby. If the team had only found one rapid star, it would
have been impossible to determine whether its speed was the result of a large
and close central mass or if that star is a runaway moving at a rapid pace in a
straight path — absent of any central mass.
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- Spotting and measuring the different
velocities and directions of seven stars allowed this determination to be made.
The measurements revealed a centralized mass equivalent to 8,200 suns, while
visual inspections of the region revealed no objects that resemble stars. That
is exactly what would be expected if a black hole was located in this region,
determined to be "light-months" wide.
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- The fact that our galaxy has matured enough
to have grown a supermassive black hole at its heart means it has probably
outgrown the stage of possessing many intermediate-mass black holes of its own.
This one exists in the Milky Way because the cannibalization of its original
galaxy happened to curtail its growth processes.
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- We now have confirmation that Omega Centauri
contains an intermediate-mass black hole.
At a distance of about 18,000 light-years, this is the closest known
example of a massive black hole.
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- That doesn't really change the status of Sgr
A* as the closest supermassive black hole to Earth, or Gaia BH1's status of the
closest stellar-mass black hole to Earth — but it provides some reassurance
that scientists are on the right track when considering how our central black
hole became such a cosmic titan in the first place.
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September 28, 2024 BLACKHOLES -
newest ones found? 4566
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--------------------- --- Saturday, September 28,
2024
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